1. Field of the Invention
The apparatus of the present invention relates generally to material transfer devices. The material transferred might include, but not be limited to, semiconductor wafers, such as silicon and Gallium Arsenide, semiconductor packaging substrates, such as High Density Interconnects, semiconductor manufacturing process imaging plates, such as masks or reticles, and large area display panels, such as Active Matrix LCD substrates.
2. Description of the Prior Art
The transfer of delicate silicon wafers or the like between a plurality of work stations or locations in the manufacture of semiconductor devices presents unique handling problems. Usually such transfer is performed by articulated arm transfer devices which operate within a vacuum environment which is remotely controlled. Consequently, it is important to be able to sense whether or not a wafer is present on the end effector of the transfer device. The silicon wafers are very delicate and have highly polished surfaces, and so it is desirable that the presence thereof be detected without contacting them.
There are numerous devices described in the prior art for transferring silicon wafers. For example:
U.S. Pat. Nos. 4,666,366 and 4,909,701 disclose wafer transfer handling apparatus having an articulated arm assembly which extends and retracts in a "froglike" motion to transfer an object such as a wafer between a plurality of locations.. Two articulated arms are operatively coupled such that when one arm is driven by a motor the articulated arms extend and retract in a "froglike" or "frogkick" type of motion. A platform is coupled to the arms and has the object to be transferred disposed thereon.